With so many people making a living on social media these days, the line between real life and advertising is more fuzzy than ever. When an Instagram star with hundreds of thousands of followers gushes about a hot new product, do they really just love it, or is there something else at play (like Amazon’s new social media influencer program)?

Dozens of social media influencers recently got letters from the FTC saying to stop hiding the fact they’re shilling products.

According to reports, more than 90 celebrities, athletes, and other influencers received mailed notifications reminding them they’re supposed to be “clearly and conspicuously” stating when they’re being paid to talk about a product. The FTC says this is the first time they have reached out directly to social media influencers to make sure they’re aware of laws.

The FTC Endorsement Guide makes it clear that if there’s a “material connection” between someone and an advertiser (a connection that affects the weight of the endorsement), that connection needs to be made clear. But quite often, it’s not.

A specific example the FTC pointed out was on Instagram, where influencers may include a disclosure noting a paid ad, but place it after the first three lines of a post. That means another user would never see that disclosure unless they click the “more” button. Also highlighted was the tendency of users to post a hashtag like #ad after a long string of hashtags, making it much less visible, or using ambiguous hashtags like “Thanks [brand],” or “#partner.”

The letters came from the FTC combing popular Instagram posts about brands or products, and picking out the ones they felt were unclear. Of course, the users that received letters were by far not the only ones being ambiguous, they’re just some of the most high profile offenders.